I have created a small test case which gets at the heart of one of these spurious warnings, namely the one for libavfilter/vf_swapuv.c.
Here is the ticket on the GCC Bugzilla: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66422 Note that as of the moment, -Warray-bounds appears quite broken on GCC (especially on -O3), and the bugzilla is full of bug reports on this. On Thu, Jun 4, 2015 at 12:16 PM, James Almer <jamr...@gmail.com> wrote: > On 04/06/15 10:08 AM, Ganesh Ajjanagadde wrote: >> On Thu, Jun 4, 2015 at 7:00 AM, Michael Niedermayer <michae...@gmx.at> wrote: >>> On Wed, Jun 03, 2015 at 10:05:54PM -0400, Ganesh Ajjanagadde wrote: >>>> While compiling ffmpeg, I noticed a bunch of -Warray-bounds warnings. >>>> I think it would be great if ffmpeg could be built warning-free, and >>>> -Warray-bounds seems to be one of the biggest culprits. Nevertheless, >>> >>>> -Warray-bounds is quite useful in most cases. >>> >>> how many of the warnings shown are real and how many are false >>> positives (in some version not neccessarily the latest of FFmpeg) >>> ? >> >> So I checked out n2.5 release. There are too many warnings to quickly >> audit all of them. >> Nevertheless, I went through about 6 instances (randomly selected), >> and found all of them to be false positives. >> Basically, there is a basic pattern to all of these warnings: >> struct foo { >> int bar[MAX_BAR]; >> int num_bar; >> }; // could have other declarations as well >> >> // in usage >> int set_foo(foo* my_foo) { >> my_foo->num_bar = get_num_bar(); >> if (num_bar > MAX_BAR) >> return -1; >> } >> >> int loop_over(const foo* my_foo) { >> int i; >> for(i = 0; i < foo->num_bar; i++) { >> // do something with foo->bar[i] >> // this triggers the warning: GCC tries to do a constant >> propagation to verify array in bounds, since it knows MAX_BAR, i.e >> foo->bar is an array. >> // However, it can't do deep enough analysis to verify that in >> set_foo, num_bar is sanitized to ensure proper in bounds access. >> } >> } > > Could you make a bug report about this on https://gcc.gnu.org/bugzilla/? > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
